We report on a case of secondary lymphoblastic leukemia L3 in a patient treated with chemo- radiotherapy for a previous Hodgkin's disease. The typical chromosome translocation t(8;14) was found in association with a translocation t(9;19) and a marker chromosome 1, dup(1q). The same marker chromosome had been detected in a few cells of peripheral blood 2 years before the onset of the acute leukemia and may represent a proliferation-associated change, responsible for the initiation of the process of leukemogenesis.